A semiconductor device having a metal oxide semiconductor (MOS) transistor and a bipolar transistor formed on one semiconductor substrate is disclosed, for example, in Japanese Patent Laid-Open No. 2001-60634 (Patent literature 1: U.S. Pat. No. 6,365,932 B1). FIG. 15 is a conventional semiconductor device disclosed in Patent literature 1 for illustrating a section of a semiconductor device 90.
The semiconductor device 90 shown in FIG. 15 is a composite IC that an active element and a passive element are formed on one semiconductor substrate 1. The semiconductor device 90 is a device for a controller of automotive vehicles, and drives load of a fuel injector (solenoid valve) or the like. The semiconductor device 90 has circuitry such as UpDrain MOSFET 8, NPN transistor 9, CMOS 10 and the like in an integrated manner.
The semiconductor device 90 in FIG. 15 uses Silicon On Insulator (SOI) board 1 as a semiconductor substrate. The SOI board 1 is manufactured by putting together substrates, and has a layered structure that a thin silicon layer 4 is disposed on top of a p-type silicon board 2 with a silicon oxide film 3 interposed therebetween. A trench 7 is formed on the silicon layer 4, and a silicon oxide film is formed on the inner wall surface of the trench 7, and a poly-silicon is filled up in the trench 7. A lot of island sections are formed by the trench 7, and nMOS and pMOS constituting the UpDrain MOSFET 8, the NPN transistor 9, the CMOS 10 are formed on each of the islands. Each of the UpDrain MOSFET 8, the NPN transistor 9 and CMOS 10 in the semiconductor device 90 is a single sided electrode element that has a pair of electrodes for driving those elements only on a silicon layer 4 side surface on the semiconductor substrate 1.
As the semiconductor device 90 shown in FIG. 15, the SOI board 1 having the silicon oxide film 3 buried by pasting two substrates is used for various kinds of uses such as the speedup of a semiconductor element formed thereon, the increased density of integration or the like.
On the other hand, the semiconductor device 90 made of the SOI board 1 with two substrates pasted together has factors such as an increased number of processing steps for die-mounting, implementing as a package and the like, which leads to production costs increase.
A method to control the increase of the production cost of the semiconductor device which has a pasted substrates is disclosed in Japanese Patent Laid-Open No. 2001-144173 (Patent literature 2: U.S. Pat. No. 6,879,029 B2). According to the method in Patent literature 2, the semiconductor devices which adopt element isolation structure can be produced without using a pasted SOI substrates, thereby enabling a simplified manufacturing process and preventing an increase of production cost.
The SOI board having the buried oxide film is suitable for the formation of the single sided electrode element such as the semiconductor device 90 as shown in FIG. 15, and the speedup and high density integration are enabled by the insulation separation trench that reaches the oxide film for separation with insulation. On the other hand, the SOI board having the buried oxide film prevents the electric current from flowing in a board cross sectional direction by the buried oxide film. On this account, the SOI board having the buried oxide film is used as a device such as a vertical metal oxide semiconductor transistor element and an IGBT element for large current electricity supply, and is not suitable for forming a double sided electrode element that has a pair of the electrodes for driving the device distributed on both sides of the semiconductor substrate surface. Therefore, many of these vertical metal oxide semiconductor transistor elements and IGBT elements are formed as one chip, and it is difficult to integrate these elements with other elements, thereby leading to production costs increase.